I assure you it's his IP address. He recently managed to figure out how to register at Network54 and has begun posting at BWW (under the name "Ant"). BWW displays the IP address. If you don't believe me, go and have a look at BWW.

Of course he could login from elsewhere (at work, say) which would be a problem, or by using a proxy (which wouldn't be a problem because he's too dumb to figure out how to do that).